Auxiliary-Free Replica Shadows: Efficient Estimation of Multiple Nonlinear Quantum Properties
Q. Y. Liu, Zihao Li, Xiao Hui Yuan, Huangjun Zhu, You Zhou · Physical Review Letters · 2026
Efficient estimation of nonlinear properties is a significant yet challenging task in quantum information processing and many-body physics. Current methodologies often suffer from an exponential sample complexity or require auxiliary qubits and deep quantum circuits. To address these limitations, we propose an efficient auxiliary-free replica shadow (AFRS) framework, which leverages the power of joint entangling operations on a few input replicas while integrating the mindset of shadow estimation. We rigorously prove that AFRS can offer exponential improvements in estimation accuracy compared with the conventional shadow method and facilitate the simultaneous estimation of various nonlinear properties, unlike the destructive swap test. Additionally, we introduce an advanced local-AFRS variant tailored to estimating local observables with constant-depth quantum circuits, significantly simplifying the experimental implementation. Our Letter paves the way for efficient and practical estimation of nonlinear properties on near-term quantum devices.